The invention is generally directed to a driving apparatus and driving method for controlling heat generating elements on a thermal print head.
Various methods have been previously utilized to prevent deterioration of the print quality due to the accumulation of heat in a thermal head caused when the thermal head is continuously used for a period of time without any stops. Japanese Patent Publication No. 48631/80 discloses a method of determining the energizing time by storing the preceding data for each dot (i.e., that is the data that was printed at the previous printing location of the dot). Japanese Patent Publication No. 18507/82 discloses a method of changing the energizing time for the print head with a driving frequency. These methods are generally called "history controlling methods" because they operate based on the prior printing history of the print head.
A conventional method of printing forwards data to a drive IC of a thermal head after it has been processed by a central processor unit (CPU). However, when a thermal printer is operated at high speed, the CPU cannot process the information quickly enough and does not maintain the speed of operation required. Therefore, this method which utilizes the processing powers of the CPU encounters problems in high-speed thermal printer operations.
In addition, Japanese Patent Laid-Open No. 158476/86 discloses a preheat controlling method wherein the thermal head is preheated immediately before the driving data when the next driving data requires the printing of a dot and combines a driving signal reduction due to the past driving histories of the print head. However, this preheating method has a problem, that is, the dot density is reduced after a blank has been printed.
Accordingly, there i a need for a print controlling apparatus and printing method for producing high speed printing on a serial type thermal printer and maintaining constant dot density regardless of the prior printing history of the thermal head.